This invention relates to a cable television signal distribution network, and is particularly concerned with what is termed a "hybrid fiber coax network", in which a conventional coaxial cable network for distribution of television signals is supplemented by optical fiber transmission paths and other equipment for communications of additional television and/or other signals, which may include bidirectional signals in digital form.
Cable television distribution networks are well known. In such networks, analog television signals are carried to customers via a branched coaxial distribution cable which includes bridger amplifiers, line extenders, and customer taps. Each television signal occupies a 6 MHz channel at a frequency from about 50 MHz to about 450 MHz or more. The upper frequency is limited by the bandwidth of the bridger amplifiers and line extenders and the attenuation of the coaxial cable, which as is well known increases with increasing frequency and cable distance.
There is an increasing desire for additional capacity in cable television distribution networks. This includes a desire for additional broadcast television signals especially in compressed digital form, additional facilities including for example video-on-demand (VOD) and near-VOD services (e.g. movies broadcast with stepped starting times), and a desire for transmission of control information in the opposite, upstream, direction via the network. There is also a desire to provide bidirectional transmission capabilities for transmission of arbitrary types of signals at various bit rates, for example for computer communications and for voice or telephone communications.
In addition, it is desired for security and commercial reasons to be able to deliver to each customer premises only those signals which are intended for that customer premises. For example, downstream signals may include confidential (e.g. banking) information which is to be delivered to a particular customer and not to other customers, and broadcast information (e.g. paid-for television programs) which is to be delivered only to specific customer premises authorized to receive such information.
Furthermore, it is important to ensure that, in the event of a fault in or tampering with equipment in the customer premises, upstream transmission from other customer premises is not disrupted. It is also necessary to ensure that noise or interference arising in the wiring at a customer premises is not communicated upstream where it could detract from communications on the cable network, and does not detract from or interfere with the downstream digital signals and television signals, this being particularly significant for the distribution of the various signals using existing customer premises wiring.
Various prior television signal distribution arrangements have been provided or proposed to meet some of these needs. Generally, such proposals do not sufficiently address the demand for upstream bandwidth especially for bidirectional transmission capabilities, and do not address the problems of upstream noise or interference originating from the many customer premises which may be connected in such arrangements.
For example, Zimmerman et al. U.S. Pat. No. 3,581,209 issued May 25, 1971 and entitled "Cable Television Program Capacity Enhancement" discloses a network having taps for individual or groups of customers in which channels for delivery to a customer are selected from a larger number of distributed channels. The arrangement uses bandpass filters and mixers for frequency changing. The taps are not addressable.
Fung U.S. Pat. No. 3,987,398 issued Oct. 19, 1976 and entitled "Remote Disconnect-Reconnect Tap For Cable Television Systems" discloses an arrangement in which taps are addressed using DTMF signals for remotely switching on and off cable service to customers, and also discloses an upstream feedback channel.
Ost U.S. Pat. No. 4,268,859 issued May 19, 1981 and entitled "High Security Cable Television Access System" discloses a cable television arrangement in which taps are switched on and off remotely by pulse sequences for selectively controlling delivery of paid-for programs.
Stern et al. U.S. Pat. No. 4,367,557 issued Jan. 4, 1983 and entitled "Wired Broadcasting Systems" discloses an arrangement in which addressable taps are controlled remotely by RF signals and power supply signals to control switches for each customer for selectively jamming broadcast channels.
A presentation by Jack Terry entitled "Future Directions--Broadband ISDN Access--Alternative Technologies and Delivery Systems" in December 1991 at IEEE ISDN '91, Tucson, Ariz. and published in IEEE Communications Magazine, August 1992 discusses various ways in which cable television networks may evolve using digital transmission with QAM (quadrature amplitude modulation) and optical fiber transmission.
None of these prior arrangements or proposals is sufficient to meet all of the needs described above.
Accordingly, an object of this invention is to provide an improved cable television signal distribution network.